These teachings relates to various embodiments of a reflective optical imager design that has an external entrance pupil and is telecentric in image space.
In many optical imaging systems, it is desirable to provide an external entrance pupil that is located outside the optical imaging system and between the source and the optical imaging system. Such an arrangement is difficult to achieve as a result of tradeoffs between the distance between the entrance pupil and the optical imaging system, or equivalently the entrance pupil relief, and the optical aberrations that result from the lack of symmetry about an optical stop that an external pupil introduces. Unlike other optical imaging systems that have a degree of symmetry about the optical stop, odd-order aberrations such as, but not limited to, optical distortion, coma, and lateral chromatic aberration cannot be substantially corrected in these types of optical imaging systems.
There is a need for optical designs, with at least one reflective element, that have an external entrance pupil and can correct for aberrations. There is also a need, with at least one reflective element, for optical designs that have an external entrance pupil and are telecentric in image space.